Copolysters plasticized with polymeric plasticizer for shrink film applications

ABSTRACT

Disclosed is a shrink film containing a copolyester having a minimum crystallization half-time of at least 8.6 minutes and a polyester plasticizer having a weight-average molecular weight of 900 to 12,000 g/mol. The polyester plasticizer includes (i) a polyol component comprising residues of a polyol having 2 to 8 carbon atoms, and (ii) a diacid component comprising residues of a dicarboxylic acid having 4 to 12 carbon atoms.

FIELD OF THE INVENTION

The invention generally relates to copolyester-based shrink films.

BACKGROUND OF THE INVENTION

A plasticizer is a polymer additive that serves to increase thepolymer's flexibility, elongation, or ease of processing. It istypically added during the compounding process of the polymer andinteracts with the polymer only physically. The most commonly measuredphysical effects of a plasticizer include melt viscosity, elasticmodulus, and glass transition.

One common class of plasticizers is based on phthalates. Phthalateplasticizers, such as dioctyl phthalate (DOP) and di-2-ethylhexylphthalate (DEHP), are widely used in polyvinyl chloride (PVC) productsfor medical delivery systems, children's toys, baby devices, and shrinkfilm.

Shrink film or heat-shrink film is a polymer film that shrinks in one ormore directions when heat is applied. To give the polymer film itsshrinkability, the film is stretched when it is above Tg of the polymerto orient the molecules from their initial random pattern. Cooling thefilm sets its characteristics until it is reheated. Reheating causes thefilm to shrink back towards its initial dimensions.

Unlike PVC shrink film, phthalate plasticizers do not work in polyestershrink film mainly due to compatibility and stability issues. Certaincopolyesters, without any plasticizer, can be converted into shrinkfilm, but they suffer from two main disadvantages. One disadvantage isthat a copolyester film without a plasticizer has a high shrink on-settemperature. Because of the high shrink on-set temperature, the filmwill not finish shrinking completely in a steam tunnel, especially on ahigh-speed line in which the dwell time in the tunnel is short. Theother disadvantage is that such a film has a high shrink force. If usedas a container label, the high shrink force can cause wrinkles in thefilm as well as distort the container's shape. Two U.S. patents haveaddressed these disadvantages.

U.S. Pat. No. 5,589,126 claims a polyester shrink film with 1 to 10weight percent of a plasticizer selected from a C₄ to C₂₀ alkyl ester ofan epoxidized fatty acid having 12 to 20 carbon atoms. In oneembodiment, the plasticizer is selected from the group consisting ofoctyl epoxy soyate, epoxy tallates, epoxidized soybean oil, epoxidizedlinseed oil, triphenyl phosphate, neopentyl glycol dibenzoate,glycerine, vegetable oil, and mineral oil.

U.S. Pat. No. 5,824,398 claims a polyester shrink film containing 1 to10 weight percent of a plasticizer selected from a C₅ to C₃₅monoglyceride prepared from the reaction of glycerol and a fatty acidhaving 4 to 30 carbon atoms.

These two patents address the plasticizer compatibility issue, but donot entirely solve the stability issue. In other words, the plasticizertends to separate from the polymer matrix and migrate to the surface ofa film, especially at higher processing temperatures. This is also aprevailing problem for plasticized PVC.

Another patent (U.S. Pat. No. 6,362,306) discloses a polyester designedto have optimal shrink on-set temperature and ultimate shrinkage tosatisfy full-body labeling and steam tunnel operation. Generally,polymers having a high diethylene glycol (DEG) content, may result in amore brittle film which may limit high-speed tentering and down-gauging.

In view of the above, there is a need in the art for polyester-basedshrink films that do not suffer from compatibility and stability issueswith plasticizers and that do not require high DEG content.

The present invention aims to address this need as well as others, whichwill become apparent from the following description and the appendedclaims.

SUMMARY OF THE INVENTION

The invention is as set forth in the appended claims.

Briefly, in one aspect, the present invention provides a shrink film.The shrink film comprises (a) a copolyester having a minimumcrystallization half-time (t_(1/2) min) of at least 8.6 minutes, and (b)a polyester plasticizer having a weight-average molecular weight (M_(w))of 900 to 12,000 g/mol. The polyester plasticizer comprises (i) a diolcomponent comprising residues of a diol having 2 to 8 carbon atoms, and(ii) a diacid component comprising residues of a dicarboxylic acidhaving 4 to 12 carbon atoms.

In another aspect, the present invention provides a method of making ashrink film. The method comprises (I) preparing a mixture comprising:(a) a copolyester having a minimum crystallization half-time (t_(1/2)min) of at least 8.6 minutes; and (b) a polyester plasticizer having aweight-average molecular weight (M_(w)) of 900 to 12,000 g/mol; (II)forming a film from the mixture; and (III) stretching the film to form ashrink film. The polyester plasticizer comprises (i) a diol componentcomprising residues of a diol having 2 to 8 carbon atoms, and (ii) adiacid component comprising residues of a dicarboxylic acid having 4 to12 carbon atoms.

DETAILED DESCRIPTION OF THE INVENTION

It has been surprisingly discovered that polyester shrink films with thedesired shrinkage characteristics can be obtained using a polymericpolyester plasticizer. The polyester plasticizer is capable of providingboth compatibility and high temperature stability with copolyester-basedmaterials. The polyester plasticizer can lower the glass transition andthus reduce the shrink on-set temperature of the resulting film. Thefilm's shrink force can also be improved by adjusting the amount of theplasticizer. The plasticized film remains clear, which makes it idealfor use in shrink film applications. Unlike polyester shrink filmscontaining high DEG content, the plasticized film of the invention ismuch stronger and can be produced, down-gauged, converted, and appliedat a much higher speed without film breakage.

The shrink film according to the invention comprises (a) a copolyesterhaving a minimum crystallization half-time (t_(1/2) min) of at least 8.6minutes, and (b) a polyester plasticizer having a weight-averagemolecular weight (M_(w)) of 900 to 12,000 g/mol.

Any copolyester can be used in this invention provided that its minimumcrystallization half-time is at least 8.6 minutes. Crystallizationhalf-times can be measured using a differential scanning calorimeteraccording to the following procedure. A sample of 10.0 mg of thecopolyester is sealed in an aluminum pan and heated at a rate of 320°C./min to 290° C. and held for 2 minutes in a helium atmosphere. Thesample is then cooled immediately at a rate of 320° C./min to anisothermal crystallization temperature ranging from 140° C. to 200° C.with a 10° C. interval. The crystallization half-time at eachtemperature is then determined as the time needed to reach the peak onthe exothermic curve. The minimum crystallization half-time is thetemperature at which the crystallization rate is the fastest.

Unless the context clearly suggests otherwise, the terms “polyester” and“copolyester” are used interchangeably herein. The term “polyester” isintended to include “copolyesters” and is understood to mean a syntheticpolymer prepared by the polycondensation of one or more difunctionalcarboxylic acids (or diacids) with one or more difunctional hydroxylcompounds (or diols). Typically, the difunctional carboxylic acid is adicarboxylic acid and the difunctional hydroxyl compound is a dihydricalcohol such as, for example, glycols and diols.

The term “residue” means any organic structure incorporated into apolymer through a polycondensation reaction involving the correspondingmonomer. The term “repeating unit” means an organic structure having adicarboxylic acid residue (or diacid component) and a diol residue (ordiol component) bonded through a carbonyloxy group. Thus, thedicarboxylic acid residues may be derived from a dicarboxylic acidmonomer or its associated acid halides, esters, salts, anhydrides, ormixtures thereof. The term “base film” means an extruded, unstretchedfilm.

The copolyester may be semi-crystalline or amorphous, preferablyamorphous. The copolyester contains repeat units from a dicarboxylicacid and a diol, based on 100 mole percent of dicarboxylic acid residuesand 100 mole percent of diol residues, respectively.

The diacid component preferably contains at least 50 mole percent of theresidues of an aromatic dicarboxylic acid having 8 to 14 carbon atoms.The copolyester may optionally be modified with up to 50 mole percent,based on 100 mole percent of dicarboxylic acid residues, of the residuesof one or more different dicarboxylic acids other than an aromaticdicarboxylic acid, such as saturated aliphatic dicarboxylic acids having4 to 12 carbon atoms and cycloaliphatic dicarboxylic acids having 8 to12 carbon atoms. Specific examples of dicarboxylic acids includeterephthalic acid, phthalic acid, isophthalic acid, naphthalenedicarboxylic acid, 1,4-cyclohexane dicarboxylic acid, cyclohexanediacetic acid, diphenyl-4,4′-dicarboxylic acid, succinic acid, glutaricacid, adipic acid, azelaic acid, sebacic acid, and the like. Thepolyester may be prepared from one or more of the above dicarboxylicacids.

It should be understood that use of the corresponding acid anhydrides,esters, and acid chlorides of these acids is included in the term“dicarboxylic acid.”

The diol component preferably contains at least 80 mole percent of theresidues of a diol containing 2 to 10 carbon atoms. In addition, thediol component may optionally be modified with up to 20 mole percent,based on 100 mole percent of diol residues, of the residues of one ormore other diols. Specific examples of diols include ethylene glycol,diethylene glycol, triethylene glycol, propane-1,3-diol,butane-1,4-diol, 2,2-dimethylpropane-1,3-diol (neopentyl glycol),2,2,4,4,-tetramethyl-1,3-cyclobutanediol, pentane-1,5-diol,hexane-1,6-diol, 1,4-cyclohexanedimethanol, 3-methyl-pentanediol-(2,4),2-methylpentanediol-(1,4), 2,2,4-tri-methylpentane-diol-(1,3),2-ethylhexanediol-(1,3), 2,2-diethylpropane-diol-(1,3),hexanediol-(1,3), 1,4-di-(hydroxyethoxy)-benzene,2,2-bis-(4-hydroxycyclohexyl)-propane,2,4-dihydroxy-1,1,3,3-tetramethyl-cyclobutane,2,2-bis-(3-hydroxyethoxyphenyl)-propane,2,2-bis-(4-hydroxypropoxyphenyl)-propane, and the like. The polyestermay be prepared from one or more of the above diols.

The polyester may also contain small amounts of trifunctional ortetrafunctional co-monomers such as trimellitic anhydride,trimethylolpropane, pyromellitic dianhydride, pentaerythritol, and otherpolyester forming polyacids or polyols generally known in the art.

In one embodiment, the copolyester comprises (i) a diacid componentcomprising at least 50 mole percent of residues of terephthalic acid,naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid,isophthalic acid, or mixtures thereof; and (ii) a diol componentcomprising at least 80 mole percent of residues of a diol containing 2to 10 carbon atoms. Preferably, the diacid component of the copolyestercomprises at least 80 mole percent of the residues of terephthalic acid,naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid,isophthalic acid, or mixtures thereof. And preferably, the diolcomponent of the copolyester comprises the residues of ethylene glycol,1,4-cyclohexanedimethanol, diethylene glycol, neopentyl glycol,2,2,4,4-tetramethyl-1,3-cyclobutanediol, or mixtures thereof.

In another embodiment, the copolyester comprises (i) a diacid componentcomprising at least 80 mole percent of terephthalic acid residues, and(ii) a diol component comprising at least 80 mole percent of theresidues of ethylene glycol and 1,4-cyclohexanedimethanol. In yetanother embodiment, the copolyester comprises (i) a diacid componentcomprising at least 80 mole percent of terephthalic acid residues, and(ii) a diol component comprising at least 80 mole percent of theresidues of ethylene glycol, 1,4-cyclohexanedimethanol, and diethyleneglycol. In yet another embodiment, the copolyester comprises (i) adiacid component comprising at least 80 mole percent of terephthalicacid residues, and (ii) a diol component comprising at least 80 molepercent of residues of ethylene glycol and neopentyl glycol. In yetanother embodiment, the copolyester comprises (i) a diacid componentcomprising at least 80 mole percent of terephthalic acid residues, and(ii) a diol component comprising at least 80 mole percent of theresidues of 1,4-cyclohexanedimethanol and2,2,4,4-tetramethyl-1,3-cycobutanediol.

Copolyesters useful in the present invention can have an inherentviscosity of 0.5 to 1.2 dL/g. Preferably, the copolyester has aninherent viscosity of 0.6 to 0.9 dL/g as measured at 25° C. using 0.50grams of polymer per 100 mL of a solvent consisting of 60% by weight ofphenol and 40% by weight of tetrachloroethane. Copolyesters useful inthe present invention can also have a glass transition temperature of40° C. to 150° C., preferably 50° C. to 100° C., and more preferablyfrom 50° C. to 90° C.

The copolyester may be prepared by conventional polycondensationprocedures well-known in the art. Such processes include directcondensation of the dicarboxylic acid(s) with the diol(s) or by esterinterchange using a dialkyl dicarboxylate. For example, a dialkylterephthalate such as dimethyl terephthalate is ester interchanged withthe diol(s) at elevated temperatures in the presence of a catalyst. Thepolyesters may also be subjected to solid-state polymerization methods.Suitable methods include the steps of reacting one or more dicarboxylicacids with one or more glycols at a temperature of about 100° C. to 315°C. at a pressure of about 0.1 to 760 mm Hg for a time sufficient to forma polyester. See U.S. Pat. No. 3,772,405 for methods of producingpolyesters, the disclosure of such methods which is incorporated hereinby reference.

The copolyesters useful in the present invention may be obtainedcommercially from Eastman Chemical Company.

The polyester plasticizer for use in the present invention has aweight-average molecular weight (M_(w)) of 900 to 12,000 g/mol.Preferably, the plasticizer has a M_(w) of 1,000 to 5,000 g/mol.

The plasticizer comprises (i) a diol component comprising the residuesof a diol having 2 to 8 carbon atoms, and (ii) a diacid componentcomprising the residues of a dicarboxylic acid having 4 to 12 carbonatoms.

Suitable diols containing from 2 to 8 carbons atoms include ethyleneglycol, 1,2- or 1,3-propanediol; 1,2- or 1,3- or 1,4-butanediol;diethylene glycol; and dipropylene glycol.

Suitable dicarboxylic acids may be represented by the formulaHO(O)CRC(O)OH where R is selected from the group consisting of linearand branched alkylene radicals containing from 2 to 10 carbon atoms andphenylene. Specific examples of such dicarboxylic acids include succinicacid, glutaric aid, adipic acid, azelaic acid, sebacic acid, isophthalicacid, orthophthalic acid, terephthalic acid, benzene-1,2-dicarboxylicacid, benzene-1,4-dicarboxylic acid, and mixtures thereof. Anhydrides ofthese diacids can readily be used depending on cost and availability.

In one embodiment, the polyester plasticizer comprises residues ofphthalic acid, adipic acid, or mixtures thereof; and residues of1,2-propanediol, 1,3-butanediol, 1,4-butanediol, or mixtures thereof.

The plasticizers according to the invention can, in general, be made byreacting one or more diols, glycols, and/or polyols with one or morecyclic or aliphatic organic acids containing two or more acidfunctionalities until the desired molecular weight is obtained asdetermined by viscosity measurements or any other generally acceptablemethod. The molecular weight of the polymer can be controlled by cappingthe unreacted acid or alcohol functionality at the end of the polyesterchains using either mono-functional alcohols or monobasic carboxylicacids until the desired hydroxyl and/or acid number of the product isreached. Typical hydroxyl numbers of the polyester plasticizers canrange from 0 to 40 mg KOH/g, and the acid numbers or acid values canrange from 0 to 50 mg KOH/g and more typically from 1 to 5 mg KOH/g.

The capping agents can be chosen from any number of readily availablealcohols or acids. Suitable capping alcohols can contain 2 to 18 carbonatoms and can be linear or branched. Suitable monobasic acid cappingagents include those containing 2 to 22 carbons and can be any number offatty acids containing C₈ to C₂₂ carbons or other common acids such asacetic acid or 2-ethyl hexanoic acid. Anhydrides, such as aceticanhydride, can be used in place of the acid.

The plasticizers useful in the present invention are also availablecommercially under the name Admex™ from Eastman Chemical Company.

The shrink film according to the invention may be prepared by thefollowing method. Before preparing a mixture of the copolyester and theplasticizer, the copolyester, the plasticizer, or both may firstoptionally be dried in an atmosphere of dried air or dried nitrogen, orunder reduced pressure.

Next, the plasticizer can be mixed with the copolyester by any suitablemelt blending process such as batch mixing, single screw, or twin-screwextrusion. Preferably, the plasticizer is injected into the melt of thecopolyester using a liquid or solid pumping system. Thecopolyester/plasticizer mixture may also be prepared by adding theplasticizer to the polyester in the polymerization after polymerizationis essentially complete. After completing the melt compounding and uponexiting the extruder, the extrudate may be shaped into a film.Alternatively, the extrudate may be withdrawn in strand form and cutinto pellets, or may be formed directly into pellets.

The pellets, prepared above, may be used as a concentrate, which ismixed with additional quantities of the copolyester. Methods for mixingthe concentrate pellets with the copolyester pellets include feeding theconcentrate pellets with an additive feeder and mechanically mixing thecopolyester and concentrate pellets. The copolyester/concentrate blendsmay then be dried, melt blended, and extruded into a film. Preferably,this film (before stretching) is visually clear.

Alternatively, the copolyester/concentrate blends may be formed into afilm by calendering as disclosed in, e.g., U.S. Pat. No. 6,068,910. Ofcourse, other conventional methods of film formation may be used aswell.

The shape of the film is not restricted in any way. For example, it maybe a flat sheet or a tube. Next, the film is stretched, for example, ineither the machine direction, the transverse direction, or both from 2to 6 times the original measurements.

The film may be stretched by any usual method, such as the rollstretching method, the long-gap stretching method, the tenter-stretchingmethod, and the tubular stretching method. With use of any of thesemethods, it is possible to conduct biaxial stretching in succession,simultaneous biaxial stretching, uni-axial stretching, or a combinationof these. With the biaxial stretching mentioned above, stretching in themachine direction and transverse direction may be done at the same time.Also, the stretching may be done first in one direction and then in theother direction to result in effective biaxial stretching. Preferably,stretching of the film is done by preliminarily heating the film 5° C.to 80° C. above its glass transition temperature (T_(g)). Morepreferably, the film is preliminarily heated to 10° C. to 20° C. aboveits T_(g). Preferably, the stretch rate is from 5 to 20 inches (12.7 to50.8 cm) per second.

Generally, the shrink film according to the invention may contain from0.01 to 10 weight percent of the polyester plasticizer. Preferably, theshrink film contains from 0.1 to 5 weight percent of the polyesterplasticizer. Generally, the shrink film may contain from 90 to 99.99weight percent of the copolyester. Preferably, the shrink film containsfrom 95 to 99.9 weight percent of the copolyester.

In a preferred embodiment, the shrink film according to the inventionhas a shrinkage of 30 to 80% in the transverse direction when submergedin a 95° C. water bath for 10 seconds.

In another preferred embodiment, the shrink film according to theinvention has a thickness of 25 to 75 micrometers.

In yet another preferred embodiment, the shrink film according to theinvention has a shrink stress in the transverse direction of less than16 MPa when measured at 400° F.

The shrink film of the invention may further comprise one or moreadditives in amounts that do not adversely affect the resultingproperties of the film. Examples of additives include antioxidants, meltstrength enhancers, chain extenders, flame retardants, fillers, acidscavengers, dyes, colorants, pigments, anti-blocking agents, flowenhancers, impact modifiers, antistatic agents, processing aids,mold-release additives, plasticizers, slip agents, stabilizers, waxes,UV absorbers, optical brighteners, lubricants, pinning additives,foaming agents, nucleators, glass beads, metal spheres, ceramic beads,carbon black, cross-linked polystyrene or acrylic beads, and the like.Colorants, sometimes referred to as toners, may be added to impart adesired neutral hue and/or brightness to the polyester blends.Representative examples of fillers include calcium carbonate, talc,clay, mica, zeolites, wollastonite, kaolin, diatomaceous earth, TiO₂,NH₄Cl, silica, calcium oxide, sodium sulfate, and calcium phosphate.Titanium dioxide and other pigments or dyes, may be included, forexample, to control whiteness of films, or to make colored films.

As used herein, the indefinite articles “a” and “an” mean one or more,unless the context clearly suggests otherwise. Similarly, the singularform of nouns includes their plural form, and vice versa, unless thecontext clearly suggests otherwise.

While attempts have been made to be precise, the numerical values andranges described herein should be considered to be approximations. Thesevalues and ranges may vary from their stated numbers depending upon thedesired properties sought to be obtained by the present invention aswell as the variations resulting from the standard deviation found inthe measuring techniques. Moreover, the ranges described herein areintended and specifically contemplated to include all sub-ranges andvalues within the stated ranges. For example, a range of 50 to 100 isintended to include all values within the range including sub-rangessuch as 60 to 90 and 70 to 80.

This invention can be further illustrated by the following examples ofpreferred embodiments thereof, although it will be understood that theseexamples are included merely for purposes of illustration and are notintended to limit the scope of the invention. Unless otherwiseindicated, all percentages are by weight.

EXAMPLES

Tables 1 and 2 below list the plasticizers and copolyesters,respectively, used in the following examples.

TABLE 1 Plasticizer Plasticizer M_(w) Identifier Type (g/mol) RawMaterials Structure P1 Polyester   936 phthalic acid — 1,2-propanediol1,4-butanediol P2 Polyester  2,848 adipic acid — 1,2-propanediol1,4-butanediol P3 Polyester  3,217 adipic acid — 1,2-propanediol1,4-butanediol P4 Polyester  4,739 adipic/ — phthalic acids1,2-propanediol 1,3-butanediol P5 Polyester  5,249 adipic acid —1,3-butanediol P6 Polyester  5,391 adipic acid — 1,3-butanediol P7Polyester 11,703 adipic acid — 1,2-propanediol 1,4-butanediol P8Dibenzoate   314 —

  diethylene glycol dibenzoate (DEGDB) P9 Polyester 14,000 (Mn =10,000)

  caprolactone

  (C₆H₁₀O₂)_(n) P10 Polyester  2,000 (Mn)

  caprolactone

  (C₆H₁₀O₂)_(n)

TABLE 2 Copolyester TPA EG CHDM DEG NPG TMCD Identifier (mol %) (mol %)(mol %) (mol %) (mol %) (mol %) M1 100 65 23 12 0 0 M2 100 69 31 0 0 0M3 100 38 62 0 0 0 M4 100 88 12 0 0 0 M5 100 72 0 0 28 0 M6 100 0 65 0 035

In Table 2, TPA=terephthalic acid, EG=ethylene glycol,CHDM=1,4-cyclohexandimethanol, DEG=diethylene glycol, NPG=neopentylglycol, and TMCD=2,2,4,4-tetramethyl-1,3-cyclobutanediol.

Examples 1-13

A 10 wt % plasticizer concentrate was prepared by injecting plasticizerP2 into a melt of copolyester M2 in a co-rotating twin-screw extruderusing a liquid pumping system. The extrudate was then pelletized andused as a concentrate for mixing with copolyesters M1, M2, and M3 atseveral blending ratios to obtain the desired shrinkage characteristics.

A 2.5-inch OD screw extruder with an electrostatic pinning unit was usedto cast a nominal 10-mil (254 microns) or less base film. The base filmwas then stretched in the transverse direction (TD) at stretch ratio of5× and line speed of 50 fpm. All formulations contained 1 wt % of anantiblock agent, PETG C0235 available from Eastman Chemical Company. Allof the stretched film samples had a nominal thickness of 50 microns,except for Examples 12 and 13, which had a nominal thickness of 40 and25 microns, respectively. The formulations and tentering temperaturesfor each sample are displayed in Table 3.

TABLE 3 Amount of Net Plasticizer Plasticizer Preheat/Stretching/Example Concentrate Content Annealing Temp. No. Copolyester (wt %) (wt%) (° F.) 1 M1 0 0 175/175/165 2 M1 10 1 175/175/165 3 M1 20 2175/175/165 4 M2 0 0 175/175/165 5 M2 10 1 180/180/165 6 M2 20 2175/175/165 7 M2 30 3 170/170/165 8 M3 0 0 210/210/165 9 M3 10 1190/190/165 10 M3 20 2 180/180/165 11 M3 30 3 175/175/165 12 M2 20 2175/175/165 13 M2 20 2 175/175/165

The tentering temperatures shown in Table 3 were adjusted based on theformulations to obtain a visually clear film (see Table 4 below). Ingeneral, for a certain polymer, a plasticizer may permit stretching afilm at a lower temperature than would be possible without theplasticizer and to maintain low haze. Table 3 shows that copolyesterswith a higher plasticizer content can be stretched at lowertemperatures.

Examples 14 (Comparative)

A base film was made from copolyester M1 compounded with 10 wt % ofplasticizer P8, a low molecular weight plasticizer, using the proceduresof Examples 1-13.

Example 15

A base film was made from copolyester M2 compounded with 10 wt % ofpolymeric plasticizer P2, using the procedures of Examples 1-13.

Film samples from Examples 1-15 were visually inspected for clarity.Their inherent viscosities, glass transition temperatures (Tg), andthermal stability were measured and reported in Table 4 below.

TABLE 4 Temp. at 10 wt % Temp. at Inherent Loss 10 wt % Loss VisualViscosity Tg in Air in Nitrogen Example No. Clarity (dL/g) (° C.) (° C.)(° C.) 1 clear 0.712 69 403.2 412.3 2 clear 0.707 68 403.6 411.4 3 clear0.689 63 404.6 408.4 4 clear 0.738 81 408.0 412.8 5 clear 0.728 75 405.1415.8 6 clear 0.712 71 402.7 409.8 7 clear 0.698 66 399.8 411.5 8 clear0.716 85 396.6 409.8 9 clear 0.702 77 396.9 409.2 10 clear 0.691 72398.1 409.5 11 clear 0.675 67 397.4 407.8 12 clear 0.711 70 404.9 407.913 clear 0.707 71 401.0 407.3 14 clear 0.664 36 294.1 302.5 15 clear0.661 43 396.2 401.9Inherent Viscosity

Inherent viscosity (IhV) was measured at 25° C. using 0.5 grams ofsample per 100 mL of a solvent consisting of 60% by weight of phenol and40% by weight of tetrachloroethane.

The IhV degradation for all samples seemed to be reasonable as displayedin Table 4. The plasticizer concentrate had an initial low IhV of 0.661dL/g (Example 15). The resulting IhV would be logically lower if ahigher amount of plasticizer concentrate were added. All samples had anIhV of around 0.7 dL/g, which is acceptable for a shrink film.

Glass Transition Temperature

The primary function of a good plasticizer is to reduce the Tg of thepolymer. All Tg's were measured in a DSC by heating the sample to 280°C. at 20° C./min, quenching to −20° C., and then heating to 280° C.again. The Tg was taken from the 2^(nd) heating cycle in nitrogenatmosphere for three polymer series M1, M2 and M3 shown in Table 8.

By linear regression, the Tg reduction by adding plasticizer concentrate(PZ conc.) in three different polymers can be expressed by equations(1)-(3) below:Tg=−0.3096×PZ conc. %+69.143 (Examples 1-3 for M1 series)  (1)Tg=−0.481×PZ conc. %+80.369 (Examples 4-7 for M2 series)  (2)Tg=−0.5723×PZ conc. %+83.461 (Examples 8-11 for M3 series)  (3)

It is desirable to know these correlations, as they allow a film to bemade with a desired Tg. For example, to match the 70° C. Tg ofcopolyester M1 using a copolyester M2, the weight % of the plasticizerconcentrate can be calculated using equation 2 and found to be 20.Similarly, it would take about 30 wt % of the plasticizer concentrate incopolyester M3 to achieve a similar Tg using equation 3 above. Theplasticizer effectiveness increases with increasing CHDM content in thecopolyester, as indicated by the magnitude of the negative slope in theequations above. Shrink films with a Tg ranging from 50° C. to 90° C.are preferable, especially when a steam shrink tunnel is employed.

Thermal Stability

Thermal degradation, in air and in nitrogen, was conducted to examine ifthere were any significant weight loss associated with variousplasticizer loading levels in the different polymers. ASTM D3850-12 wasused as the testing method. The heating rate was 20° C./min from 20° C.to 600° C. The results are shown in Table 4 above.

At 10% weight loss, there was little or no discernible temperaturedifference between the neat polymer and the same polymer with differentplasticizer concentrations. These results indicate that there was noadditional weight loss due to plasticizer instability at hightemperatures. The temperature during typical compounding and extrusionprocesses would generally not exceed 300° C.

On the other hand, copolyester M1 with 10 wt % of the low molecularweight plasticizer P8 (DEGDB, M_(W)=314, Example 14) started to loseweight at 200° C. in air. It lost 10 wt % at 294° C. and 20 wt % at 400°C. These results indicate that DEGDB is an efficient plasticizer forcopolyesters, but is not thermally stable.

Shrinkage Testing

The oriented films from Examples 1-11 were cut into 100 mm×100 mm squaresamples. The samples were tested in a water bath at various temperaturesfor 10 seconds. The percent shrinkage was then calculated using thefollowing equation:shrinkage %=100−final sample length (mm).

From this data, the shrinkage versus temperature curve (or shrink curve)in the transverse direction (TD) can be constructed. The shrink on-settemperature is defined as the temperature where the TD shrink curve andtemperature axis intersect. An ideal shrink curve for “low” temperaturepackaging should have a shrink on-set temperature of around 55° C. Forgeneral shrink packaging, the shrink on-set temperature should be around65° C. For hot-fill applications, the shrink on-set temperature shouldbe above 75° C. to prevent the label from sticking due to residual heat,e.g., hot tea shrink labeling.

The shrinkage results are shown in Tables 5-7 below.

Table 8 shows some additional properties for the films from Examples1-13.

TABLE 5 Water Bath Example 1 Example 2 Example 3 Temperature TDShrinkage TD Shrinkage TD Shrinkage (° C.) (%) (%) (%) 60 not measurednot measured 6 65  1 12 28 70 25 34 39 75 44 48 48 80 55 58 56 85 67 6762 90 74 72 69 95 76 76 73

TABLE 6 Example 5 Example 7 Water Bath Example 4 TD Example 6 TDTemperature TD Shrinkage Shrinkage TD Shrinkage Shrinkage (° C.) (%) (%)(%) (%) 65 2 1 3 4 70 3 7 13 20 75 15 31 42 46 80 41 52 60 60 85 61 6869 67 90 72 75 74 71 95 78 78 76 75

TABLE 7 Example 9 Example 11 Water Bath Example 8 TD Example 10 TDTemperature TD Shrinkage Shrinkage TD Shrinkage Shrinkage (° C.) (%) (%)(%) (%) 65 1 1 1 5 70 1 2 5 18 75 2 10 27 42 80 10 33 50 51 85 27 48 5857 90 34 53 62 60 95 42 58 66 63

TABLE 8 Copolyester/ Shrink On-Set Shrink Stress Force Machine DirectionAverage Total Surface Example Plasticizer Temp. at 400° F. Elongation atModulus Energy Number Combination (° C.) (MPa) Break (%) (MPa) (dyne/cm)1 M1 65 6.3 3.9 2922 47.2 2 M1 + 1% P2 63 4.6 3.6 2828 48.1 3 M1 + 2% P255 3.6 3.2 2584 48.1 4 M2 70 15.4 364 3835 47.4 5 M2 + 1% P2 69 13.1 3093812 47.9 6 M2 + 2% P2 68 9.1 351 3544 48.7 7 M2 + 3% P2 67 7.4 343 354149.0 8 M3 75 11.2 80 3108 48.2 9 M3 + 1% P2 72 11.1 79 3474 47.3 10 M3 +2% P2 66 10.5 63 3364 42.9 11 M3 + 3% P2 62 6.9 60 3180 48.4 12 M2 + 2%P2 65 10.3 345 3674 49.6 (40 micron film) 13 M2 + 2% P2 64 11.0 288 443449.2 (25 micron film) Examples 1-12 have a nominal film thickness of 50microns.

With a Tg of 70° C. and a shrink on-set temperature of 65° C., polymerM1 is very useful in shrink film applications. For even lowertemperature shrink packaging, polymer M1 can be plasticized with theplasticizers of the invention, resulting in lower on-set temperatureshrink curves, as shown in Table 5.

As seen from Table 5, the shrinkage at 70° C. increased with increasingplasticizer content for the M1 polymer. These films were all stretchedunder the same tentering conditions (see Table 3). As seen from Table 4,the shrinkage increase correlates with the Tg reduction of the polymerby the plasticizer.

As seen from Table 8, the shrink on-set temperature decreased withincreasing plasticizer content. With 20 wt % of the plasticizerconcentrate or just 2 wt % net plasticizer content in the shrink film,the shrink on-set temperature of Example 3 dropped to 55° C. from 65° C.of neat polymer (Example 1). This lower shrink on-set temperature wouldallow shrink sleeves to finish quicker in a shrink tunnel. This isdesirable for packaging heat sensitive goods such as milk, etc. Onecaution, however, is that this shrink film must be safeguarded fromoverheating during storage and transportation, especially in the summertime of hot climate areas.

With a higher Tg of 80° C., neat polymer M2 is not ideal for shrink filmapplications, in part, because it has a high shrink on-set temperature,which results in partially finished shrink labels in high-speedproduction lines. The shrink film reacts to heat too slowly and does nothave enough dwell time to finish shrinkage. Making the tunnel longer orto run the line slower is not desired in today's output orientedproduction.

But by adding the plasticizer concentrate into polymer M2, differentshrink properties can be obtained as illustrated by the shrink curvedata in Table 6. The shrink characteristics of polymer M1 (Table 5,Example 1) can be closely approximated by using 30 wt % of theplasticizer concentrate (3 wt % net plasticizer content) in the polymerM2 (Table 6, Example 7).

As seen in Table 8, the shrink on-set temperatures of Examples 1 and 7were almost the same. There is an advantage of plasticized polymer M2versus polymer M1. A plasticized polymer M2 film is much stronger than afilm from polymer M1, thereby enabling high-speed operation intentering, slittering, printing, sleeving, and dispensing with much lessfilm breakage. Film breakage during any conversion step is detrimentalto production efficiency.

Similarly, neat polymer M3 is unsuitable for certain shrink filmapplications because of its even higher Tg of 85° C. Stretched film frompolymer M3 has a high shrink on-set shrink temperature of 75° C. and alow ultimate shrinkage (see Table 7, Example 8). Such a film would notperform well in a steam tunnel for labeling high contour bottles.However, it would perform rather well in a hot air tunnel for low shrinkapplications such as batteries or wine caps. It can also be used safelyin hot-fill shrink labeling to prevent label sticking due to residualheat in the container's contents, such as from hot tea or coffee,resulting in softening of the label that can occur with polymers oflower Tg.

Polymer M3 can be plasticized with a plasticizer, and the resultingshrink curves are shown in Table 7. Even though the shrinkage increasedwith increasing plasticizer content, the plasticized polymer M3 stilldid not have enough ultimate shrinkage for full body labeling. However,it can be used for bottles with less contour and high temperature shrinklabeling, such as required for hot-fill applications.

Shrink Force

As seen in Table 8, the addition of plasticizer reduced the shrink forceof the film. The shrink stress was calculated by dividing the peak forceat 400° F. over the cross-sectional area of the sample. In polymer M2examples, the shrink force was high in the absence of plasticizer andwas reduced significantly with the addition of plasticizer, as shown inTable 8. In polymer M3 examples, the plasticizer can also bring down theshrink force at high loading, such as 30 wt % of the concentrate orabove.

Film Breakage

Web or film breaking is an issue in every step of shrink filmproduction, conversion, and application. Improper drying in filmextrusion usually contributes to the majority of the problem. Film aging(free volume relaxation) can also exacerbate the web-breaking problem.Solvent attack and excessive web tension can cause problems in theprinting process.

Ideally, a shrink film should be strong enough to accommodate allpotential tensions without a web break. One way to measure the ductilityof the TD stretched film is by testing the machine direction (MD)tensile elongation at break at 350 mm/min according to ASTM 882. Theresults for the shrink films from Examples 1-13 are shown in Table 8.

As seen in Table 8, the elongation at break in the MD was relatively lowfor polymer M1 and was not significantly influenced by the amount ofplasticizer additive. Part of the effect may have come from the lowerIhV obtained at higher plasticizer concentrate loadings.

Compared to a high DEG polymer like M1, polymer M2 has much better MDelongation at break, as shown in Table 8. While adding plasticizer mayhave lowered the elongation slightly, partially from the IhV reduction,the elongation remained approximately ninety times greater than theelongation of polymer M1. The effect of the plasticizer on polymer M3was similar, as indicated in Table 8. Polymer M3 has a 10-20 timesbetter result than polymer M1 in MD elongation at break.

Modulus (Flexural Rigidity)

Table 8 shows the average modulus of MD and TD moduli, which isproportional to flexural rigidity of the film.

High rigidity prevents sleeve labels from collapsing in high-speedapplications. In principle, an effective plasticizer should make a rigidfilm more flexible, similar to plasticized PVC film. The polymericplasticizer according to the invention, however, did not alter themodulus of copolyester significantly, as shown in Table 8.

Surface Energy

Printability is a highly desirable property for shrink film packaging.Though the surface energy is not the only indicator for printability, itwill indicate if the plasticizer migrates to the surface and reduces thetotal surface energy.

As seen in Table 8, there is no evidence that the plasticizers accordingto the invention changed the surface energy of the stretched films.Since the plasticizer is polymeric, its migration to the film surfacewould be very slow, if at all.

From the thermal stability data (Table 4), the affinity between thepolymer matrix and the plasticizer seemed to be very strong, asindicated by little if any discernible weight loss at highertemperatures.

Down-Gauging

As previously noted, adding DEG to a copolyester can lower its Tg andimprove the shrinkage properties of films made from the copolyester. Theresulting composition, however, tend to be more brittle due to thehigher DEG content. Thus, films made from polymer M1 are more prone toweb-break when stretching in a tenter, printing in a press, and/ordispensing in a sleeve applicator. This is especially true for thinnerfilms, e.g., below 40 micron in thickness. To enable down-gaugingwithout losing productivity, polymer M2 with the addition of plasticizerseems to be a promising alternative, as shown in Table 9 below where a25-micron polymer M2 film was successfully produced with good shrinkage.Also, as seen in Table 9, the shrinkage and the shrink on-settemperature of the down-gauged film (25 microns) with the plasticizermimic those of higher gauge films (40 and 50 microns).

TABLE 9 Example 6 Example 12 Example 13 Water Bath TD Shrinkage of TDShrinkage of TD Shrinkage of Temperature 50 Micron Film 40 Micron Film25 Micron Film (° C.) (%) (%) (%) 65 3 4 8 70 13 23 37 75 42 49 51 80 6061 65 85 69 70 72 90 74 73 76 95 76 77 78Copolyester Composition

A shrink film is typically amorphous even though it is highlyorientated. Crystallization induced by orientation will reduce theultimate shrinkage of the film. A film with less than 30% ultimateshrinkage at 95° C. has less utility in shrink applications. CopolyesterM4 was used to demonstrate the concept of crystallization half-time.

The M4 polymer has an IhV of 0.68 dL/g and a minimum half-timecrystallization (t₁₁₂ min) of 517 seconds (8.6 minutes). Crystallizationhalf-times were measured using a Perkin-Elmer Model DSC-2 differentialscanning calorimeter. 10.0 mg of each sample were sealed in an aluminumpan and heated at a rate of 320° C./min to 290° C. and held for 2minutes in a helium atmosphere. The sample was then cooled immediatelyat a rate of 320° C./min to an isothermal crystallization temperatureranging from 140° C. to 200° C. with a 10° C. interval. Thecrystallization half-time at each temperature was then determined as thetime needed to reach the peak on the exothermic curve. The minimumcrystallization half-time is the temperature where the crystallizationrate is the fastest.

Examples 16-21

Shrink films were made by blending the polymer M4 with 0-50 wt % of aplasticizer concentrate, which contained 10 wt % of plasticizer P2 inpolymer M2, following the procedures of Examples 1-13, except that thefilms were stretched 4× at 85° C.

As seen in Table 10, at a lower percentage of the plasticizerconcentrate (0-30 wt %), the film crystallized after being stretched.The ultimate shrinkage at 95° C. of these films was in the lower 30%range, which is the practical lower limit for shrink film applications.

The CHDM content increased with increasing plasticizer concentration dueto the high CHDM-containing plasticizer concentrate. As seen in Table10, the oriented film was more amorphous and less crystalline when theresulting CHDM content in the film was 18 mol % or higher. The Tgcontinued to decrease with increasing plasticizer content. Thus, theshrinkage at 75° C. increased with increasing plasticizer content,although the ultimate shrinkage at 95° C. of all the samples remainedmore or less in the lower 30% range. Based on the shrinkage requirementsfor a shrink film, any polyester can be used in this invention providedthat its minimum crystallization half time is at least 8.6 minutes.

TABLE 10 Net Plasticizer CHDM Crystal- Shrinkage Shrinkage ExampleContent Tg Content linity at 75° C. at 95° C. Number (wt %) (° C.) (mol%) (%) (%) (%) 16 0 78 12 24 2 34 17 1 74 14 23 8 30 18 2 70 16 18 10 3019 3 67 18 4 20 32 20 4 63 20 7 24 32 21 5 60 22 3 26 34

Examples 22-25

A polymer containing 28 mole % NPG and 72 mole % EG (polymer M5) wasalso blended with the plasticizer concentrate, formed into shrink film,and tested. Table 11 shows that adding a polymeric plasticizer accordingto the invention reduced the Tg of the polymer M5. Table 12 reports theTD shrinkage of the films made from the polymer M5 stretched 5× at 85°C. using a Bruckner film stretcher. The data in Table 12 shows that thepolymeric plasticizer according to the invention also works well withNPG-containing polymers.

TABLE 11 Plasticizer Polymer M5 Concentrate Net Plasticizer ContentContent Content Tg Example No. (wt %) (wt %) (wt %) (° C.) 22 100 0 0 7823 90 10 1 74 24 80 20 2 70 25 70 30 3 68

TABLE 12 Example 23 Example 24 Example 25 Water Bath Example 22 TD TD TDTemperature TD Shrinkage Shrinkage Shrinkage Shrinkage (° C.) (%) (%)(%) (%) 65 0 0 18 28 70 4 18 48 44 75 30 40 54 54 80 50 54 60 54 85 6866 64 61 90 72 70 70 70 95 76 74 70 70

Examples 26-36

Films (approximately 254 microns thick) were prepared from blendscontaining the polymers and plasticizers listed in Table 13. Theirvisual clarity and Tg were determined and are reported in Table 13.

Polycaprolactone (PCL) is a polyester having a Tg of about −60° C. PCLcan be used as a polymeric plasticizer for PVC.

Example 26 is a base film made of copolyester M2 with 10 wt % ofplasticizer P9 (PCL, M_(n)=10,000). The resulting film was very hazy.

Example 27 is a base film made of copolyester M2 with 10 wt % ofplasticizer P10 (PCL, M_(n)=2,000). The resulting film was also hazy.

Based on the haziness of the resulting films, PCL is not compatible withcopolyester M2.

Examples 28-30 are base films made of copolyester M6 (Tg=120° C.) withplasticizer P2 (M_(w)=2,848). As seen in Table 13, the combination iscompatible based on the clarity of the films. The Tg's of Examples 29-30are below 90° C., which indicates that shrink films made from theseblends would be particularly useful in a steam shrink tunnel.

As seen from Example 15 in Table 4 and Examples 31-36 in Table 13, thepolyester plasticizers having a M_(w) from 1,000 to 12,000 according tothe invention are compatible with polymer M2. The film in Example 36 wasslightly hazy and showed the least Tg reduction, which indicate arelationship between the compatibility and the molecular weight of thesepolyester plasticizers with polymer M2.

TABLE 13 Plasticizer Amount Example No. Copolyester Plasticizer (wt %)Clarity Tg (° C.) 26 M2 P9 10 Hazy 78 27 M2 P10 10 Hazy 64 28 M6 P2 1Clear 106 29 M6 P2 5 Clear 85 30 M6 P2 10 Clear 75 31 M2 P1 10 Clear 5415 M2 P2 10 Clear 43 32 M2 P3 10 Clear 54 33 M2 P4 10 Clear 64 34 M2 P510 Clear 64 35 M2 P6 10 Clear 53 36 M2 P7 10 Slightly 68 Hazy

To summarize, Table 14 illustrates the pass (◯), fair (Δ), or fail (×)scores for all of these examples. The four selection criteria are thecrystallization, thermal stability, compatibility, and glass transitiontemperature as described above. Note that samples are less useful asshrink film materials if they do not pass all criteria. Examples 14 and15 have their Tg's below 50° C. at 10 wt % plasticizer. However,reducing the plasticizer content in these blends can increase their Tg.Thus, Examples 14 and 15 were not marked with “X” in the Tg column, eventhough Example 14 failed the thermal stability test. Crystallizationhalf-time is a selection criterion for the copolyester. Thermalstability and compatibility are selection criteria for the plasticizer.Compatibility and glass transition are selection criteria for thepolymer/plasticizer blends.

TABLE 14 Example Thermal Compatibility/ Tg = Nos. t_(1/2) > 8.6 minStability Clarity 50 to 90° C.  1-13 ◯ ◯ ◯ ◯ 14 ◯ X ◯ ◯ 16-18 ◯ ◯ ◯ ◯19-21 ◯ ◯ ◯ ◯ 22-25 ◯ ◯ ◯ ◯ 26-27 ◯ not tested X ◯ 28 ◯ not tested ◯ X29-30 ◯ ◯ ◯ ◯ 15 and 31-35 ◯ ◯ ◯ ◯ 36 ◯ ◯ Δ ◯

Unless otherwise specified, the following ASTM methods were used.D2857-96 for inherent viscosity, D3418 for glass transition temperature,D3850 for thermal stability, D2732 for shrinkage, D882 for elongation atbreak and modulus, and D5946 for surface energy.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

We claim:
 1. A single-layer shrink film comprising: (a) a copolyesterhaving a minimum crystallization half-time (t_(1/2) min) of at least 8.6minutes; and (b) a polyester plasticizer having a weight-averagemolecular weight (M_(w)) of 900 to 12,000 g/mol, wherein the polyesterplasticizer comprises: (i) a diol component comprising residues of adiol having 2 to 8 carbon atoms; and (ii) a diacid component comprisingresidues of a dicarboxylic acid having 4 to 12 carbon atoms, wherein theshrink film has a glass transition temperature of from 50 to 90° C.,wherein the shrink film has a thickness of 25 to 75 micrometers, andwherein the shrink film has a shrinkage of 30 to 80% in the transversedirection when submerged in a 95° C. water bath for 10 seconds.
 2. Theshrink film according to claim 1, wherein the copolyester comprises: (i)a diacid component comprising at least 50 mole percent of residues ofterephthalic acid, naphthalenedicarboxylic acid,1,4-cyclohexanedicarboxylic acid, isophthalic acid, or mixtures thereof;and (ii) a diol component comprising at least 80 mole percent ofresidues of a diol containing 2 to 10 carbon atoms, wherein the diacidcomponent is based on 100 mole percent of total diacid residues in thecopolyester and the diol component is based on 100 mole percent of totaldiol residues in the copolyester.
 3. The shrink film according to claim2, wherein the diacid component of the copolyester comprises at least 80mole percent of residues of terephthalic acid, naphthalenedicarboxylicacid, 1,4-cyclohexanedicarboxylic acid, isophthalic acid, or mixturesthereof.
 4. The shrink film according to claim 2, wherein the diolcomponent of the copolyester comprises residues of ethylene glycol,1,4-cyclohexanedimethanol, diethylene glycol, neopentyl glycol,2,2,4,4-tetramethyl-1,3-cyclobutanediol, or mixtures thereof.
 5. Theshrink film according to claim 2, wherein the copolyester comprises: (i)a diacid component comprising at least 80 mole percent of terephthalicacid residues; and (ii) a diol component comprising at least 80 molepercent of residues of ethylene glycol and 1,4-cyclohexanedimethanol. 6.The shrink film according to claim 2, wherein the copolyester comprises:a diacid component comprising at least 80 mole percent of terephthalicacid residues; and (ii) a diol component comprising at least 80 molepercent of residues of ethylene glycol, 1,4-cyclohexanedimethanol, anddiethylene glycol.
 7. The shrink film according to claim 2, wherein thecopolyester comprises: (i) a diacid component comprising at least 80mole percent of terephthalic acid residues; and (ii) a diol componentcomprising at least 80 mole percent of residues of ethylene glycol andneopentyl glycol.
 8. The shrink film according to claim 2, wherein thecopolyester comprises: (i) a diacid component comprising at least 80mole percent of terephthalic acid residues; and (ii) a diol componentcomprising at least 80 mole percent of residues of1,4-cyclohexanedimethanol and 2,2,4,4-tetramethyl-1,3-cyclobutanediol.9. The shrink film according to claim 1, wherein the diol component ofthe polyester plasticizer comprises residues of ethylene glycol,1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol,1,4-butanediol, diethylene glycol, dipropylene glycol, or mixturesthereof.
 10. The shrink film according to claim 1, wherein the diacidcomponent of the polyester plasticizer comprises residues of succinicacid, glutaric acid, adipic acid, azelaic acid, sebacic acid,isophthalic acid, orthophthalic acid, terephthalic acid, or mixturesthereof.
 11. The shrink film according to claim 1, wherein the polyesterplasticizer comprises residues of phthalic acid, adipic acid, ormixtures thereof; and residues of 1,2-propanediol, 1,3-butanediol,1,4-butanediol, or mixtures thereof.
 12. The shrink film according toclaim 1, wherein the polyester plasticizer has a M_(w) of 1,000 to 5,000g/mol.
 13. The shrink film according to claim 1, which comprises from0.01 to 10 weight percent of the polyester plasticizer.
 14. The shrinkfilm according to claim 1, which comprises from 0.1 to 5 weight percentof the polyester plasticizer.
 15. The shrink film according to claim 1,which is visually clear before stretching.
 16. The shrink film accordingto claim 1, which has a shrink stress in the transverse direction ofless than 16 MPa when measured at 400° F.
 17. A method of making asingle-layer shrink film, the method comprising: (I) preparing a mixturecomprising: (a) a copolyester having a minimum crystallization half-time(t_(1/2) min) of at least 8.6 minutes; and (b) a polyester plasticizerhaving a weight-average molecular weight (M_(w)) of 900 to 12,000 g/mol,(II) forming a film from the mixture; and (III) stretching the film toform a shrink film having a thickness of 25 to 75 micrometers, whereinthe polyester plasticizer comprises: (i) a diol component comprisingresidues of a diol having 2 to 8 carbon atoms; and (ii) a diacidcomponent comprising residues of a dicarboxylic acid having 4 to 12carbon atoms, and wherein the shrink film has a shrinkage of 30 to 80%in the transverse direction when submerged in a 95° C. water bath for 10seconds.
 18. A shrink film comprising: (a) 90 to 99.99 weight percent ofa copolyester having a minimum crystallization half-time (t_(1/2) min)of at least 8.6 minutes; and (b) a polyester plasticizer having aweight-average molecular weight (M_(w)) of 900 to 12,000 g/mol, whereinthe polyester plasticizer comprises: (i) a diol component comprisingresidues of a diol having 2 to 8 carbon atoms; and (ii) a diacidcomponent comprising residues of a dicarboxylic acid having 4 to 12carbon atoms, wherein the shrink film has a thickness of 25 to 75micrometers, wherein the shrink film has a glass transition temperatureof from 50 to 90° C., and wherein the shrink film has a shrinkage of 30to 80% in the transverse direction when submerged in a 95° C. water bathfor 10 seconds.
 19. The shrink film according to claim 18, wherein thedegree of crystallinity is 7% or less.